rollup merge of #20483: nagisa/rng-copy

* Implement (derive) `Clone` for `ChaChaRng`, `Isaac*Rng`, `StdRng` and `ThreadRng`;
* Derive `XorShiftRng` `Clone` implementation instead of implementing it explicitly.

`OsRng` is the only Rng which does not implement `Clone` or `Copy` after this patch because of its dependence on `Reader`.

r? @huonw I guess?

1 files changed, 2 insertions, 1 deletions

diff --git a/src/libstd/rand/mod.rs b/src/libstd/rand/mod.rs
index aa28c8266d1..cadaae5de5c 100644
--- a/src/libstd/rand/mod.rs
+++ b/src/libstd/rand/mod.rs
@@ -245,7 +245,7 @@ pub mod reader;
 
 /// The standard RNG. This is designed to be efficient on the current
 /// platform.
-#[derive(Copy)]
+#[deriving(Copy, Clone)]
 pub struct StdRng {
     rng: IsaacWordRng,
 }
@@ -322,6 +322,7 @@ static THREAD_RNG_RESEED_THRESHOLD: uint = 32_768;
 type ThreadRngInner = reseeding::ReseedingRng<StdRng, ThreadRngReseeder>;
 
 /// The thread-local RNG.
+#[deriving(Clone)]
 pub struct ThreadRng {
     rng: Rc<RefCell<ThreadRngInner>>,
 }